for major shift in the earth climate over time:
Intense Volcanic Activity:
• Volcanoes when erupting inject a large amount of greenhouse gases into the atmosphere which can have a significant impact on the climate. The historic record shows evidence of a correlation between periods of intense volcanic activity, the level of carbon dioxide into the atmosphere and global surface temperatures.
The Milankovitch Cycles:
• They refer to the variation of the tilt of the earth's axis away from the orbital plane. The tilt varies between 22.1o and 24.5o averaging 23.5o. The obliquity changes on a cycle taking approximately 40,000 years.
• As this tilt changes, the seasons become more exaggerated. "the more tilt means more severe seasons, warmer summers and colder winters; less tilt means less severe seasons, cooler summers and milder winters."
• For an increase of 1o in obliquity, the total energy received by the summer hemisphere increases by approximately 1%
• The activity of our sun is not constant
• At periodic intervals the Sun undergoes periods of intense activity which are reflected by the apparition of Solar Spots on its surface
• Intense activity of the sun has some impacts on our climate. It remains however a small influence
Tectonic Activity: Continental Drift
• The continents are constantly moving on the surface of the earth in a process referred to as plate tectonics
• In the past the continents as we know them today were very different
• Today's continents drifted away from one major continent known as The Gondwana
• While moving across different latitudes of the planet, different areas of continents passed through different climate zones
• This is however a very slow process
Source of Information : Climate Change: A Silent Threat by Sylvain Richer de Forges